This invention relates in general to a timepiece wheel, and in particular, to a timepiece wheel having a wheel portion and pinion portion formed by forging or compressing.
Timepiece wheels are known in the art as disclosed in Japanese Laid-open Patent Publication No. 62-161076. This prior art timepiece wheel includes a wheel and pinion formed as separate components. The two components are then joined by an interference fit. A second timepiece wheel is illustrated in Laid-open Patent Publication No. 61-48869 which discloses a timepiece wheel having a pinion portion, gear portion and axis portion integrally formed of a single resin. Another timepiece wheel is known in the art as disclosed by Japanese Laid-open Patent Publication No. 61-55472 which discloses a timepiece wheel having a central hole and a base portion. A tooth portion is integrally formed on the base portion by swelling the base portion.
These prior art mechanisms have been satisfactory, however, the timepiece wheel of Japanese Laid-open Patent Publication No. 62-161076 has a gear portion in which the gear milling is made by press working a doughnut shaped plate. The gear milling of the pinion is formed by a lathing operation which is performed separately from the formation of the gear portion. The pinion is then driven into the gear portion to produce an interference fit. Accordingly, it requires 20 to 30 seconds to produce each gear portion and each pinion. An additional one to two seconds is required to assemble the completed timepiece wheel.
During operation of the timepiece wheel of Japanese Laid-open Patent Publication No. 61-48869, the wheel must be strong enough to bear the slip force of the central wheel and pinion, the force at the time of assembly or detaching the timepiece hands and the pressing force applied by the regular lever. Therefore, the wheel and pinion must be a very strong member which requires enlarging the module of the gear and pinion while increasing the thickness of the plate of the gear. Additionally, more than ten seconds is required to manufacture the timepiece wheel. Accordingly, it becomes relatively expensive to manufacture this prior art timepiece wheel due to the large processing time, expensive materials and necessity to increase the strength of the timepiece wheel by making the timepiece wheel bigger and larger.
The timepiece wheel of Japanese Laid-open Patent Publication No. 61-55472 is formed by opening a hole in the central portion of the wheel and then forming ten independent teeth on the circumference of the wheel by compressing a plate base. This structure has an advantage of requiring less processing time. However, to improve the strength of the die, each tooth is required to be enlarged. Further, the diameter of the hole is larger than the thickness of the wheel base so that when the central hole is open during manufacturing, the gear upon which the teeth should be formed around the hole must become very large. Such a gear is not suitable for the acceleration or deceleration which is required in the gear train of the timepiece. In particular, when the timepiece wheel is positioned in the front gear train, the acceleration gear train, or the deceleration gear train, because the central hole is very large, and because the front gear train always includes the broken portions formed by shearing, the torque loss at the bearing portion is large. Additionally, each tooth is formed independently so that the height of each tooth will vary during manufacturing. This variation of tooth height makes the positioning of the gear difficult at the top surface of the teeth.
Accordingly, it is desirable to provide a timepiece wheel which overcomes the shortcomings of the prior art device described above.